<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>利用类选择器画三个颜色盒子</title>
    <style>
        .red{
            width: 100px;
            height: 100px;
            /* 背景颜色 */
            background-color: red;
        }
        .green{
            width: 100px;
            height: 100px;
            /* 背景颜色 */
            background-color:seagreen;
        }
    </style>
</head>
<body>
    <div class="red">红色</div>
    <div class="green">绿色</div>
    <div class="red">红色</div>
</body>
</html>